CeO2 Loading Research Articles

Preparation of a CeO2/γ-Al2O3 composite and its catalytic degradation performance

CeO2/γ-Al2O3 composite catalyst has been prepared using CeO2 as an active component and γ-Al2O3 as a support to remove dye from wastewater by catalytic degradation. The catalytic performance of the CeO2/γ-Al2O3 sample for the degradation of methylene blue is studied under visible light irradiation. The results show the presence of γ-Al2O3 and CeO2 with a cubic fluorite structure in the CeO2/γ-Al2O3 samples synthesized at 550°C. Small CeO2/γ-Al2O3 particle and a good dispersion of CeO2 are achieved with loading of CeO2. The loading of CeO2 on γ-Al2O3 also increases the total pore volume and pore diameter, which results in a high specific surface area of 132.03 m2/g, a total pore volume of 0.74 cm3/g, and a mean pore diameter of 22.54 nm. The photocatalytic degradation efficiency of methylene blue by the CeO2/γ-Al2O3 catalyst is higher than those of CeO2 and γ-Al2O3. Under the same conditions the CeO2/γ-Al2O3 catalyst achieves 98.36% degradation at 80 min, higher 5.0% and 11.9% degradation than CeO2 and γ-Al2O3, respectively. The high efficiency is attributed to promotion of the structural and textural performance of the CeO2/γ-Al2O3 catalyst by synergistic interaction between CeO2 and γ-Al2O3. These performances promote a larger surface area, higher content of acid sites, more •OH radicals and higher redox properties of the catalyst. The catalytic reaction kinetics could be fitted by the heterogeneous Langmuir-Hinshelwood model and the pseudo-first order rated constant for kapp is 17.5×10−2, which is 1.33 and 2.5 times as big as those of CeO2 and γ-Al2O3, respectively. CeO2/γ-Al2O3 catalyst suggests promising application for practical dye pollutant treatment.

Influence of CeO2 loading on the structural, textural, optical and photocatalytic properties of single-pot sol-gel derived ultrafine CeO2/TiO2 nanocomposites for the efficient degradation of tetracycline under visible light irradiation

A single-pot surfactant-free sol-gel method is reported for the facile and bulk synthesis of ultrafine-nanospherical CeO2/TiO2 composites with different CeO2 loadings and their photocatalytic-activity for the degradation and mineralization of tetracycline (TC) under visible-light irradiation is investigated for the first time. The incorporation of CeO2 favored the controlled crystalline growth of TiO2 in its anatase phase, and their crystallinity and particle size were significantly decreased. The textural and optical properties of TiO2 were also improved with the incremental addition of CeO2 by increasing their specific surface-area and visible-light absorption respectively. The optical band gap of TiO2 decreased to 2.24 eV with the incorporation of 1% CeO2 and it further decreased to 2.21 eV with the incremental amount of CeO2. Due to the formation of heterojunction in the composite, the recombination rate of electron-hole pairs was significantly decreased. A highest TC removal efficiency of ~99% was observed for 4% CeO2/TiO2 composite for a period of 80 min of visible-light irradiation. Moreover, 88.2% TC mineralization efficiency was achieved for a period of 240 min of visible light irradiation. The enhanced catalytic-activity could be attributed to the synergy of high degree of adsorption followed by an enhanced photocatalysis at the heterointerface formed by the adjacent contact between TiO2 and CeO2. The synergistic effects of low-particle size, high surface-area, enhanced visible-light absorption, reduced band-gap, and increased life-time of the photogenerated charge-carriers through the formation of heterointerface contributed to its high photocatalytic activity. The hydroxyl and superoxide-anion radicals played a superior role in the photocatalytic process. Moreover, the composites retained its efficiency for seven-cycles of reaction without any significant-loss in its activity and structural and textural stability.

Preparation of Polyamide 6/CeO2 Composite Nanofibers through Electrospinning for Biomedical Applications

Polyamide 6 (PA6)/CeO2 composite nanofibers were prepared by electrospinning technique. The morphological, structural, and mechanical properties of the PA6/CeO2 nanofibers were investigated by using SEM, XRD, Fourier transform-infrared (FT-IR) spectroscopy, and an electronic universal tensile testing machine. SEM images revealed that the nanofibers were well oriented and had good incorporation with CeO2, the average diameter of composite fibers first decreases and then increases with the loading of CeO2. The crystallinity of fibers decreases after the addition of CeO2. The tensile strength of the fibers first increases and then decreases with the increasing concentration of CeO2. The proliferation properties of mouse macrophages and osteoblasts on the PA6/CeO2 nanofibers were analyzed by an in vitro cell compatibility test, the results show that PA6/CeO2 composite fibers is nontoxic to macrophages and osteoblasts and has good biocompatibility.

Metal oxide sub-nanoclusters decorated Ni catalyst for selective hydrogenation of adiponitrile to hexamethylenediamine

Nickel based catalysts were decorated by metal oxide (MOx = CeO2, La2O3 or MgO) and used for the selective hydrogenation of adiponitrile to hexamethylenediamine. Additional MOx sub-nanoclusters were dispersed on surface to manipulate the electron and surface structures of nickel particles. The functional role of, e.g. CeO2 decorator, was to benefit the formation of Ni-CeO2 interfaces and acted as electron donor for the Ni active sites, rather than to change the morphology, crystallization, or the H2 activation energy barrier. The d-band center calculated by Density Functional Theory was altered and close to the Fermi-level after CeO2 loading, rationally accounting for the accelerated reaction rate. The decorated CeO2 behaved like a double-edge sword. Excessive loading of ceria easily led to the coverage of Ni sites and destroyed the elaborated Ni-CeO2 synergy. By using Ni-Ce3/Al2O3 with only 3 at% CeO2, adiponitrile can be completely transformed at 90 °C in 7 MPa H2 for 3 h with 90% yield of hexamethylenediamine. The additional CeO2 also resulted in the enhanced stability of Ni catalyst, which maintains its high catalytic stability even after 5 reaction cycles.

Simultaneous removal of NO and volatile organic compounds (VOCs) by Ce/Mo doping-modified selective catalytic reduction (SCR) catalysts in denitrification zone of coal-fired flue gas

A series of Ce/Mo doping-modified V-W/Ti type catalysts were prepared by one-step impregnation method, in an attempt to realize collaborative removal of NO and volatile organic compounds (VOCs) in selective catalytic reduction (SCR) reaction zone (the temperature scope of 260–420 °C). Benzene and Toluene were used as model compounds of VOCs. A self-built experimental platform was conducted to simulate the coal-fired flue gas denitrification zone with a flue gas of 750 mL/min. Different loading amount of CeO2 (0–17.5 wt%) or MoO3 (3–7.5 wt%) and different calcination temperature (400–600 °C) during catalyst preparation were investigated. Results showed that 10.75 wt% CeO2 loading as well as 4.5 wt% MoO3 loading on V-W/Ti catalyst calcinated at 500 °C represented the best simultaneous removal effect of NO, benzene and toluene. This study provided an efficient method for pollutant reductions of coal-fired power plant.

Evaluation of thermal stability in deep geological repository and nuclear criticality safety of spent nuclear fuel vitrified in iron phosphate glass

Iron phosphate glasses with low melting temperatures of ∼1300 °C were developed to immobilize spent nuclear fuels (SNFs). The glasses have densities of ∼3.15 g/cm3 and glass transition temperatures of ∼540 °C that are high enough to endure the temperatures in geological repositories. The waste loading of CeO2 in the glass was ∼21.92 wt%, which corresponds to ∼30.38 wt% of UO2 at the same molar ratio. Normalized elemental releases from the product consistency test were well below the regulated limit of 2 g/m2. Effective neutron multiplication factor keff was 0.755, which is below nuclear criticality safety regulation (keff = 0.95). Vitrified SNF occupies one-eleventh of the repository space compared to direct disposal of the same amount of UO2, excluding left-over low-level wastes.

Preparation of Au/xCeO2-Al2O3 catalysts with enhanced catalytic properties for the selective acetylene hydrogenation

In this work, Au/Al2O3 and Au/xCeO2-Al2O3 catalysts were prepared by incipient wetness impregnation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), raman spectroscopy, temperature programmed hydrogen reduction (H2-TPR) and temperature programmed NH3 desorption and C2H2 desorption (NH3-TPD, C2H2-TPD). TEM and XRD results showed that there was no obvious difference for the structures and morphologies compared with Au/Al2O3 and Au/xCeO2-Al2O3. However, enhanced catalytic performance was found in the selective acetylene hydrogenation to ethylene. Raman spectra showed that no coke was obtained for Au/xCeO2-Al2O3. NH3-TPD confirmed that with the increase of CeO2 loading, the surface acidity was decreased and an appropriate CeO2 addition was needed for the improvement of catalytic activity. The charge transfer between metallic Au and CeO2 leads to positively charged Au (Auδ+).The basic character of CeO2 and the positively charged Au may play a positive role in the selective acetylene hydrogenation reaction. A possible reaction mechanism was proposed in this paper.

Facile synthesis of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) nanosheets for DFT supported visible photocatalysis of 2-Chlorophenol

Visible light active g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) ternary composite nanosheets were fabricated by facile co-precipitation routes. The density functional theory (DFT) computations investigated changes in geometry and electronic character of g-C3N4 with CeO2 and Fe3O4 addition. Chemical and surface characterizations were explored with XRD, XPS, SEM, TEM, PL, DRS and Raman measurements. DRS and PL spectroscopy evidenced the energy band gap tailoring from 2.68 eV for bulk g-C3N4 and 2.92 eV for CeO2 to 2.45 eV for the ternary nanocomposite. Efficient electron/hole pair separation, increase in red-ox species and high exploitation of solar spectrum due to band gap tailoring lead to higher degradation efficiency of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01). Superior sun light photocatalytic breakdown of 2-Chlorophenol was observed with g-C3N4 having CeO2 loading up to 5 wt%. In case of ternary nanocomposites deposition of 1 wt% Fe3O4 over g-C3N4/CeO2 binary composite not only showed increment in visible light catalysis as predicted by the DFT studies, but also facilitated magnetic recovery. The g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) nanosheets showed complete mineralization of 25 mg.L−1 2-CP(aq) within 180 min exposure to visible portion of sun light and retained its high activity for 3 consecutive reuse cycles. The free radical scavenging showed superoxide ions and holes played a significant role compared to hydroxyl free radicals while chromatographic studies helped establish the 2-CP degradation mechanism. The kinetics investigations revealed 2.55 and 4.04 times increased rate of reactions compared to pristine Fe3O4 and CeO2, showing highest rate constant value of 18.2 × 10−3 min−1 for the ternary nanocomposite. We present very persuasive results that can be beneficial for exploration of further potential of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) in advance wastewater treatment systems.

Enhanced visible light photocatalytic activity of CeO2@Zn0.5Cd0.5S by facile Ce(IV)/Ce(III) cycle

In this study, CeO2@Zn0.5Cd0.5S heterostructure (Ce@ZCS) is synthesized via a simple two-step hydrothermal method. The effect of CeO2 loading on the visible-light photoactivity of Zn0.5Cd0.5S is mainly investigated. It is found that Ce@ZCS shows a 1.9 times activity as high as ZCS for the MB degradation. The improved activity mainly results from the significant enhanced charge separation by CeO2, in which the electron transfer is obviously promoted by the facile Ce(IV)/Ce(III) cycle. The excited electrons of ZCS is easy to transfer to CeO2, thus obviously increasing the charge separation of ZCS. The accepted electrons by CeO2 may easily be captured by the adsorbed O2 to form O2−, and then O2− could combine with H+/H2O to form HO2, and OH. Finally, O2−, h+ and OH are confirmed as the major oxidative species in photocatalytic reaction for Ce@ZCS, and a possible photocatalytic mechanism is proposed. The cheap, efficient Ce@ZCS photocatalyst could be applied for practical waste water treatment.

The Impact of CeO2 Loading on the Activity and Stability of PdO/γ-AlOOH/γ-Al2O3 Monolith Catalysts for CH4 Oxidation

This study reports on the activity and stability of PdO/γ-AlOOH/γ-Al2O3 monolith catalysts, promoted with varying amounts of CeO2, for CH4 oxidation. Although the beneficial effects of CeO2 have been reported for powdered catalysts, this study used a cordierite (2MgO.2Al2O3.5SiO2) mini-monolith (400 cells per square inch, 1 cm diameter × 2.5 cm length; ~52 cells), washcoated with a suspension of γ-Al2O3 combined with boehmite (γ-AlOOH), followed by sequential deposition of Ce and Pd (0.5 wt.%) by wetness impregnation. The monolith catalysts’ CH4 oxidation activity and stability were assessed in the presence of CO, CO2, H2O and SO2 at low temperature (≤550 °C), relevant to emission control from lean-burn natural gas vehicles (NGVs). The CeO2 loading (0 to 4 wt.%) did not significantly impact the adhesion and thermal stability of the washcoat, but CeO2 reduced the inhibition of CH4 oxidation by H2O and SO2. The catalyst activity, measured by temperature-programmed methane oxidation (TPO) in a dry feed gas with 0.07 vol.% CH4, showed that adding CeO2 to the γ-AlOOH/γ-Al2O3 washcoat suppressed the activity of the catalysts; whereas, CeO2 improved the catalyst activity when H2O (2 and 5 vol.%) was present in the feed gas. Moreover, adding CeO2 decreased catalyst deactivation that occurred in the presence of 10 vol.% H2O and 5 ppmv SO2 at 500 °C, measured over a 25 h time-on-stream (TOS) period. The highest catalyst activity and stability for CH4 oxidation in the presence of H2O was obtained by adding 2 wt.% CeO2 to the washcoat.

A study on the effect of CeO2 addition to a Pt/TiO2 catalyst on the reverse water gas shift reaction

ABSTRACT In this study, a series of catalysts with the composition 1 wt% Pt/X% CeO2-Y% TiO2 (where X and Y range from 0 to 20%) was prepared via impregnation. The effects of different ratios of CeO2/TiO2 on the catalytic activity were examined during the reverse water gas shift reaction (RWGS). The catalytic activities of the Pt-impregnated catalysts were enhanced by increasing CeO2 loading. The activity tests, temperature-programmed reduction via H2, and step test of an elementary RWGS reaction over the catalysts confirmed that the catalytic activity depends on the number of TiO2 or CeO2 sites, which participate in the RWGS reaction, on the surface of the support.

Optimization of nickel and ceria catalyst content for synthetic natural gas production through CO2 methanation

Manufacturing of catalysts with high reaction rates at mild conditions is important for an efficient production of synthetic natural gas through the CO2 methanation process. In this work, the design of a technical catalyst based on an optimal content of Ni as active phase, CeO2 as promoter and γ-Al2O3 micro-spheres as support (dp = 400–500 μm) is evaluated. The systematic optimization of Ni, CeO2 and γ-Al2O3 content revealed that a proper balance of the positive effects that each component provided individually, was found at 25 wt% Ni, 20 wt% CeO2 and 55 wt% γ-Al2O3 content. This catalyst was stable for 120 h at 300 °C. The high loading of CeO2 is far from the classical definition of promoter and it covers the gap between the addition in a low amount as promoter and its uncompetitive use as bulk support. The highest catalytic activity was attributed to high metallic surface area (5 m2·g−1), high nickel reducibility (79% at 500 °C) and the formation of moderate basic sites that can adsorb CO2 (−65 kJ·molCO2−1). In comparison with similar research catalysts and a commercial reference, the optimum formation showed higher activity for synthetic natural gas production. Therefore, the micro-catalyst can be implemented in the micro-structured reactors that are available in the market.

Synthesis of CeO2‐loaded titania nanotubes and its effect on the flame retardant property of epoxy resin

A series of CeO2‐loaded titania nanotubes (CeO2‐TNTs) hybrid materials with different CeO2 loadings were synthesized by co‐precipitation method and then incorporated into epoxy resin (EP) to prepare CeO2‐TNTs flame‐retardant epoxy nanocomposites. Structure and morphology characterization indicated the successful synthesis of CeO2‐TNTs. The effect of CeO2‐TNTs with different CeO2 loading capacity on the flame retardance of EP was compared and analyzed by the thermogravimetric analysis, Cone and Raman. The results showed that CeO2 loading could increase the carbon residue of nanocomposites, reduce the peak heat release rate (PHRR) and total heat release (THR), and improve the fire safety of EP. The residual carbon content of EP/0.1CeO2‐TNTs sample at 700°C reached 19.8% with the lowest degradation rate, and the PHRR and THR were reduced to 680 kW/m2 and 32.9 MJ/m2, respectively. Such a significant improvement in flame‐retardant properties for EP could be attributed to the protective effect of CeO2‐TNTs.

Effect of CeO2 loading of the Ce-Al mixed oxide on ultrahigh temperature water-gas shift performance over Ce-Al mixed oxide supported Ni catalysts

The purpose of this study is to investigate and to evaluate the effect of CeO2 loading in the Ce-Al mixed oxide (CeO2-Al2O3) on physicochemical properties as well as the ultrahigh temperature water-gas shift (UHT-WGS) catalytic performance of Ni/x wt.%CeO2-Al2O3 (xCe-Al; x = 1, 3, 5, 7, and 10) catalysts. The Al2O3 (Al) and the xCe-Al supports were synthesized via the sol-gel method. The Ni/Al and Ni/xCe-Al catalysts were prepared by the incipient wetness impregnation method. The catalysts were characterized using XRD, the N2 adsorption-desorption isotherms, H2-TPD, H2-TPR, TEM and TGA/DTA. The UHT-WGS catalytic performance of these catalysts were carried out in a packed-bed tubular reactor. The results reveal that adding CeO2 to the Al2O3 support for the Ni supported catalyst increased the surface area resulting in the enhancement of nickel dispersion and reducibility of the Ni/xCe-Al catalysts. However, under certain circumstances, bulk CeO2 can separate from the support to the catalyst surface and partially cover the Ni metal in the case of high CeO2 loading. Compared to other catalysts, the Ni/5Ce-Al catalyst illustrates the highest UHT-WGS catalytic activity (CO conversion >75%) with the maintainability. This proposed composition provides the appropriate Ni-Ce-Al interaction that also suppresses the graphitic/filamentous carbon.

Supercritical CO2-assisted fabrication of CeO2 decorated porous carbon/sulfur composites for high-performance lithium sulfur batteries

Alleviating shuttle effect is vital to improve the electrochemical performance of lithium–sulfur (Li–S) batteries. Herein a nanosheet-like porous carbon (NSPC) with unique hierarchically porous structure and excellent electrical conductivity was synthesized as a host material of cathode, and highly-dispersed, electrochemically active CeO2 nanoparticles as well as sulfur was deposited onto NSPC subsequently through supercritical CO2-assisted processing to fabrticate CeO2 decorated porous carbon/sulfur (C/CeO2/S) composites. In testing Li–S batteries, the C/CeO2/S material shows an initial capacity of 1538 mAh g−1 at 0.1 C, higher than that of C/S (1194 mAh g−1). The material also exhibits excellent cycling stability (~ 729 mAh g−1 at 0.5 C after 300 cycles). The gas-like viscosity, diffusivity and surface tension of supercritical CO2, facilitate highly dispersed loading of CeO2 and sulfur on porous carbon with less agglomeration and more intimate contact with carbon to achieve higher conductivity and utilization efficiency. Moreover the electrocatalytic material CeO2 promotes and stabilizes the redox reaction of polysulfide species.

Effect of La2O3 and CeO2 loadings on formation of nickel-phyllosilicate precursor during preparation of Ni/SBA-15 for hydrogen-rich gas production from ethanol steam reforming

The importance of La2O3 or both La2O3 and CeO2 promoters on the formation of nickel phyllosilicate (Ni3Si4O12H2) as a precursor of Ni/SBA-15 for ethanol steam reforming (ESR) was investigated. The catalyst was made by a one-step modified conventional triblock copolymer synthesis method (pH-Adjustment with ammonium hydroxide). The prepared catalysts were characterized by N2 adsorption/desorption isotherms, XRD, H2-TPR, SEM-EDS and TGA-DSC techniques. The N2 adsorption/desorption isotherms identified the mesoporous nature of the catalysts and the XRD patterns of the calcined catalysts confirmed the formation of nickel-phyllosilicate structure. The H2-TPR analysis revealed that the La2O3 loading considerably increased the interaction between nickel and silica frame work of SBA-15 support. The ability of these catalysts for hydrogen production from ethanol steam reforming (ESR) was evaluated in a packed bed reactor at 650 °C. In the case of Ni/SBA-15 catalysts without and with La2O3 promoter, the ESR experiments experienced metal sintering and coke formation. Meanwhile, the catalytic activity of both La2O3 and CeO2 promoted Ni/SBA-15 catalyst (Ni-La2O3-CeO2/SBA-15) remained stable with time on stream in terms of GPR and hydrogen selectivity. The stable performance of this catalyst was explained by the strong interaction of nickel with SBA-15 promoted by La2O3 and the suppression of coke formation by CeO2.

Enhanced low‐temperature Selective Catalytic Reduction (SCR) of NOx by CuO‐CeO2‐MnOx/γ‐Al2O3 mixed oxide catalysts

A series of CuO‐MnOx‐CeO2/γ‐Al2O3 catalysts in different ratios were synthesized by a sol‐gel method with the purpose of improving the low‐temperature denitration performance (loading a transition mental oxide (MnOx, CeO2) on a CuO/γ‐Al2O3 copper‐based catalyst). The denitration performance of a low‐temperature SCR under the condition of simulated flue gas was measured using the programmed heating method in the catalytic reaction efficiency evaluation system. The denitration efficiency of the 6 % CuO‐5 % MnOx‐10 % CeO2/γ‐Al2O3 catalytic particles was maintained at over 80 % within a temperature range of 100–200 °C. The catalysts were characterized by surface area analysis (BET), x‐ray diffraction (XRD), and scanning electron microscopy (SEM). The best surface structure characteristics include the 5 % MnOx + 10 % CeO2 loading capacity of the catalyst, which was indicated by a BET analysis. The catalyst surface structure characteristics were effectively promoted by the amount of CeO2 and MnO2 loading proved by the SEM analysis. The possible mechanisms involved in SCR denitration at a low temperature were also discussed. The experimental results revealed that the catalyst granule with perfect surface characteristics and pore features was successfully synthesized by the sol‐gel method. The denitration performances were restrained by 10 % of H2O and 800 mg · m−3 of SO2, indicating that SO2 and H2O have an inhibiting effect on NOx conversion.

Syngas production via dry reforming of methane over CeO2 modified Ni/Al2O3 catalysts

Syngas production via dry reforming of methane (DRM) was experimentally investigated using Ni-based catalyst. Ni/Al2O3 modification with CeO2 addition and O2 addition in the reactant were employed in this study to suppress carbon deposition and to enhance catalyst activity. It was found that DRM performance can be enhanced using CeO2 modified Ni/Al2O3 catalyst due to CeAlO3 formation. However, an optimum amount of CeO2 loading exists to obtain the best DRM performance due to the decrease in specific surface area as the CeO2 loading increases. Without O2 addition, the reverse water-gas shift reaction plays an important role in DRM. It was found that CH4 conversion and CO yield were enhanced while CO2 conversion and H2 yield are decreased as the CO2 amount in feedstock increased in DRM. With O2 addition in the fed reactant, it was found that the methane oxidation reaction plays an important role in DRM. CH4 conversion can be enhanced by O2 addition. However, decreases in CO2 conversion and H2 and CO yields occurred due to greater H2O and CO2 productions from the methane oxidation reaction. The thermogravimetric analysis (TGA) results showed that CeO2 modified Ni/Al2O3 catalyst would have the lowest amount of carbon deposition when O2 is introduced into the reaction.

Enhancement of Electricity Generation in Single Chamber Microbial Fuel Cell Using Binuclear-Cobalt-Phthalocyanine and Cerium Oxide Co-Supported on Ordered Mesoporous Carbon as Cathode Catalyst

High cost and limited natural reserves of precious metals as oxygen reduction reduction (ORR) catalysts have hindered the practical application of microbial fuel cells (MFCs). Herein, the cost-effective catalysts were synthesized by co-doping binuclear-cobalt-phthalocyanine (Bi-CoPc) and cerium oxide (CeO2) on ordered mesoporous carbon (OMC). The catalysts Bi-CoPc/x%CeO2/OMC (x = 3, 6 and 12) with different CeO2 loading were physically characterized by Nitrogen physisorption, X-ray Diffraction, Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy, and chemically characterized by Rotary Disk Electrode analysis. The relationship between the CeO2 content and ORR activity was investigated. The optimum CeO2 loading in the Bi-CoPc/6%CeO2/OMC catalyst provided the highest Ce3+ content that are favorable for the chemisorbed oxygen. Bi-CoPc/6%CeO2/OMC led to an increased half wave potential and limiting current density and to the further decreased over-potential. It also displayed a higher electron transfer number in comparison with Bi-CoPc/3%CeO2/OMC and Bi-CoPc/12%CeO2/OMC. The electrochemical results were closely related with the voltage generation obtained in single chamber MFC (SCMFCs) with air cathode. Bi-CoPc/6%CeO2/OMC-based SCMFC generated the highest power density of 486 ± 6 mW/m2 and achieved chemical oxygen demand removal of 79.3 ± 1.5%. The voltage generation for Bi-CoPc/6%CeO2/OMC decreased only by 3.7% after 1300 h of operation, indicating its good stability in MFCs large scale application.

Promoting Effect of Cerium Oxide on the Catalytic Performance of Yttrium Oxide for Oxidative Coupling of Methane.

The promoting effect of CeO2 on the catalytic performance of Y2O3, which is moderately active catalyst, for the oxidative coupling of methane (OCM) reaction was investigated. The addition of CeO2 into Y2O3 by coprecipitation method caused a significant increase in not only CH4 conversion but also C2 (C2H6/C2H4) selectivity in the OCM reaction. C2 yield at 750 °C was increased from 5.6% on Y2O3 to 10.2% on 3 mol% CeO2/Y2O3. Further increase in the CeO2 loading caused an increase in non-selective oxidation of CH4 to CO2. A good correlation between the catalytic activity for the OCM reaction and the amount of H2 consumption for the reduction of surface/subsurface oxygen species in the H2-TPR profile was observed, suggesting the possibility that highly dispersed CeO2 particles act as catalytically active sites in the OCM reaction. The 16O/18O isotopic exchange reaction suggested that the beneficial role of CeO2 in the OCM reaction is to promote the formation of active oxygen species via the simple hetero-exchange mechanism, resulting in the promotion of CH4 activation.